1. Field of Invention
This invention relates to pressure sensitive copy sheets which are coated on at least one face with pressure-rupturable units containing a marking liquid, and interspersed and in close juxtaposition therewith larger, non-rupturable units containing kaolin particles, for the purpose of protecting the pressure-rupturable units from accidental impacts and premature color formation.
2. Description of the Prior Art
U.S. Pat. No. 3,481,759 to Ostlie, issued Dec. 2, 1969, teaches the use of discrete stilt particles which consist of the same material as is employed to encapsulate the liquid marking material. Stated otherwise, the stilt particles are composed primarily of solid encapsulating material, i.e., they contain only a small amount of the liquid.
U.S. Pat. No. 3,617,334 to Brockett et al, issued Nov. 2, 1971, teaches the use of discrete stilt particles which consist of encapsulating material having a liquid fill. That is, each of the stilt particles consists of encapsulating material containing a plurality of inert liquid droplets.
U.S. Pat. No. 3,697,323 to Brown, Jr. et al, issued Oct. 10, 1972, does not teach the use of discrete stilt particles. It is, however, considered to be of interest because it teaches, particularly in FIG. 5A, the use of a continuous binder material layer containing encapsulated liquid droplets of the marking agent, and also solid filler material bits and free spaces (voids). Kaolin is not mentined for use as the solid filler material bits; only bentonite clay is mentioned, among other substances, for such use.
U.S. Pat. No. 2,655,453 to Sandberg, issued Oct. 13, 1953, teaches the use of discrete stilt particles which are not encapsulated. The stilt particles may be composed of glass beads, rounded white silica sand, casein particles and vinyl acetate polymer material particles.
U.S. Pat. No. 3,706,593 to Miyano et al, issued Dec. 13, 1972, is of interest with respect to the protective stilt particles of the present invention. It teaches in FIG. 2 thereof microcapsules comprising a capsular material such as gelatin enclosing certain transparent inorganic particles, for example, glass or silica. There is no teaching of employing these microcapsules as a stilt material in a record sheet.
U.S. Pat. No. 3,179,600 to Brockett does not teach the use of discrete stilt particles. However, it does teach an outer capsule wall containing silica, kaolin or bentonite (note column 3, lines 70-72), which would appear to act as a protective covering against premature rupture of inner capsules containing a marking liquid.